<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        canvas {
            border: 1px solid;
        }
    </style>
</head>

<body>
    <canvas width="500" height="500" id="mycanvas"></canvas>
    <script>
         let obj = {
            bg1: "https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fimg.jj20.com%2Fup%2Fallimg%2Ftp02%2F1Z9191923035R0-0-lp.jpg&refer=http%3A%2F%2Fimg.jj20.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1661397561&t=a620034e48d31890e7e652561c79083b", bg2: "https://img2.baidu.com/it/u=1713796643,4188877777&fm=253&fmt=auto&app=138&f=JPEG?w=889&h=500", bg3: "https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fimg.jj20.com%2Fup%2Fallimg%2Ftp05%2F1Z9291TIBZ6-0-lp.jpg&refer=http%3A%2F%2Fimg.jj20.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1661397561&t=d113fcaf5515f719281a37f6e928b213"
        };

        function LoadImg(obj){
            return new Promise ((resolve) =>{
                // 获取对象的长度
                let length = 0;
                for (let key in obj){
                    length++;
                }

                // 记录图片加载好的数量
                let num = 0;
                let resObj = {};
                for (let k in obj){
                    let ImgEl = new Image();
                    ImgEl.src = obj[k];
                    ImgEl.onload = function(){
                        num++
                        resObj[k] = this;
                        if (num >= length){
                            // 所有图片加载完毕/
                            resolve(resObj);
                        }
                    }
                }
            })
        }
        let canvas = document.querySelector("#mycanvas");
        // 获取上下文 ；画笔
        let context = canvas.getContext("2d");
        LoadImg(obj).then(resObj => {
            context.drawImage(resObj['bg1'], 0, 0, 100, 100);
            context.drawImage(resObj['bg2'], 200, 200, 100, 100);
            context.drawImage(resObj['bg3'], 300, 300, 100, 100)
        })
       

    </script>
</body>

</html>